Présentations Colloques

    Oral Presentation
    Valois Remi
    Characterizing stream aquifer exchanges thanks to geophysics
    Characterizing stream aquifer exchanges is an important goal in hydrogeology as more and more models link these two units in one combined model. Indeed, assessing exchanged volumes is important in water balance and hydrogeological modeling, especially regarding water quality issues.**The site studied here is producing clear water for Bordeaux metropole from wells in the porous-fractured and karstic unit of the Oligocene limestone. Hydrodynamics and geochemistry surveys highlights connections between those wells and a stream running close by. Due to the high vulnerability of the stream, the wells were impacted by a pollution and that’s the reason why characterizing those connections with geophysics is important.**Hydrodynamics suggests such connections, but a quantitative interpretation is rapidly limited by the difficulty of isolating the effect of the stream on groundwater levels from the effect of the recharge on both aquifer and stream levels.**Geochemistry had clearly proven the existence of pathways from the stream to the wells, thanks to tracing tests and major ions analysis. Nevertheless, these surveys cannot help to locate such pathways in order to protect the wells from a polluted stream.**Electrical resistivity tomography and electrical Self-Potential profiles have been carried out in and out the stream bed. Since these methods are sensitive to water content and flow, this study shows that they could give evidences of stream aquifer connections and help to determine if the stream is gaining or loosing. These methods could also help to reduces aquifer vulnerability by locating infiltration pathways in the riverbed.**


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